Conventional lighting systems for stage, theater, architectural and display illumination include means for removably inserting various types of optical beam modifiers into the light beam to vary the color, intensity, size, shape and pattern of the beam. Thus, in a typical system, a light source produces white light which is passed, for example, through at least one dichroic filter color wheel for producing a colored light beam, a gobo wheel for imposing a selected pattern on the light beam, a light intensity wheel for varying the intensity of the light transmitted therethrough, a mechanical iris for determining beam size and a lens system for controlling light beam focus and divergence. U.S. Pat. No. 4,392,187--Bornhorst discloses several such systems.
For imposing a desired pattern on the light beam it is well known to pass the beam through a gobo, which is a template or light stencil having a predetermined pattern. Typically, gobos are formed by chemically etching the desired pattern onto stainless steel discs. The discs are supported in the projected light beam to impose upon the light passing therethrough the pattern which has been etched into the discs. It is well known, for example, from U.S. Pat. No. 4,460,943--Callahan to provide a mounting plate having a plurality of equally spaced apertures arranged around a common axis for mounting gobos within one or more of the openings. The plate is drivingly rotatable, as via a motor, about its axis to insert a selected gobo into the beam of light. U.S. Pat. No. 4,891,738--Richardson et al discloses a similar arrangement including an apertured gobo mounting plate which is rotatably driven by motor driven rollers frictionally engaging the peripheral edge of the plate. The gobos are mounted on or within holders which, in turn, are positioned within the plate apertures. The mounting plate is rotatably driven to position a selected gobo within the beam of light. In this position a motor-operated holder drive mechanism acts, through frictional contact with the rim of the holder, to rotatably drive the gobo holder in either direction at any desired speed. In this manner the plate is rotatable to position a selected gobo within the beam of light and the gobo holder is rotatable to spin the gobo holder within the beam of light. Similar functions are achieved with the gobo wheel disclosed in European Patent Application Publication No. 0 511 829 A2 in which each of a plurality of gobo holders has gear means associated with it which engages a central sun gear for simultaneously rotatingly driving all of the gobo holders.
Most typically, gobos are mounted directly, or indirectly via gobo holders, to gobo plates by spring clips. Frequently, the spring clips take the form of cantilevered spring fingers or tabs which have been formed from or affixed to the mounting plate at 120 degree intervals around the gobo. The fingers define, with the mounting plate surface, a predimensioned space into which gobos of specified thicknesses may be inserted and securely held by the spring fingers. Since most stainless steel gobos are very thin, having a thickness in the range of 2 to 10 mils, the use of spring clips having a predetermined small clearance with the plate has proven to be a reasonably effective way for mounting gobos. Recently, however, it has been found that gobos having better pattern resolution than the thin stainless steel gobos and which do not warp with heat, as do the stainless steel gobos, can be prepared by chemically etching metal coatings, such as aluminum or nickel coatings, formed on glass substrates. Due to the thickness of the glass substrates, the resulting high pattern resolution gobos have thicknesses which are up to 10 to 15 times the thickness of conventional stainless steel gobos and will not fit into the spring clips which have been dimensioned for the considerably thinner stainless steel gobos. For the same reason, gobo wheels having spring clips designed to accept the thicker glass substrate gobos cannot securely hold the thinner stainless steel gobos. This inability to securely retain thin stainless steel gobos and thicker glass substrate gobos in the same apparatus has caused and will continue to cause a serious problem in the entertainment lighting industry. As a result, there is a serious need for a gobo holder which has the ability to accept and securely hold, in a manner allowing ease of insertion, quick release and rapid interchange, gobos having a wide variety of thicknesses.